Thanks for your indulgence, but this is a question I've had for some time. A steamship has an unlimited supply of water available, but it's salty. Do they boil it anyway and just wash the boilers continuously or distill boiler water, save on maintenance but raise fuel costs?

davidwoodbury@adelphia.net

> Thanks for your indulgence, but this is a
> question I've had for some time. A steamship
> has an unlimited supply of water available,
> but it's salty. Do they boil it anyway and
> just wash the boilers continuously or
> distill boiler water, save on maintenance
> but raise fuel costs?

In the U.S. Navy, they use flash type distillers to produce fresh water which is also typical of other marine steam vessels. The ship I was an engineering officer on had two, each rated at 24,000 gallons a day which was more than sufficient since we used a closed cycle steam system -- assuming the valve maintenance and steam leaks were kept current. This water also was what the crew and embarked Marines drank. The nominal figure that the Navy uses is that each individual was allowed fifty gallons per day. This covered the galley, the laundry and personal consumption such as showers as well as drinking water. The water produced by the flash distillers is quite pure. I forget the exact figure on contamination (salt) but it was in the low parts per million. Usually the water produced by the distilling units was much softer than provided by most ports when hooked up to city water. The water had to be very pure because the higher pressure of marine boiler would greatly accelerate both chloride and O2 attack on the metal of the boiler. The boilers in my care were 600 PSI "super D" water tube boilers that held 1200 gallons of water. These boilers were good for about 27,000 horse power each without the emergency over sized sprayer plates. I served on another ship that had pressure fired boilers operating at 1200 PSI. Bottom blows could not be conducted when firing the boiler, the bottom blow would interrupt the water circulation in the boiler and could lead to tube failure. Every 168 (one week) operating hours, the boiler had to be secured, allowed to naturally cool to about 150 psi when the "mud" drum two screen wall headers were bottom blown into the ocean. Surface blows could be conducted while firing the boiler and were scheduled every 24 operating hours. Water chemistry was checked as a minimum every four hours and more often if the boiler was starting to go out of limits on any of the parameters. Also, the marine boiler is fed "deaerated" feed water. There is a large tank in which the 15 psi exhaust steam was blown through the feed water to remove any dissolved oxygen. Typically this tank would sport a paint job of the favorite brew of the lead Boiler Technician while deployed. Also, a boiler was never allowed to go cold with water in it except for pressure vessel maintenance when we had a 24 hour window, but this had to be followed by a light off. But this was considered not the preferred method, usually we had to drain the boiler. When secured in port, a "steam blanket" was cut into the boiler. Shore steam came at a nominal pressure of between 75 and 150 psi. This steam was certified and we used it to pressurize the boilers to keep O2 from entering the boiler system. We could keep a boiler under a steam blanket for seven days then we had to either drain the boiler or light it off. Usually we would "bump" the boiler by firing to operating pressure then secure it without bringing it on line to reset the clock on the steam blanket. Typically, boilers were drained when in port unless your ship is designated a "ready" ship with a requirement to get underway on some predetermined notice which is when we would use the steam blanket. As I became interested in steam locos, my previous experience with steam turbines made my hair stand-up a couple of times when I started learning about boiler management on the rails. There is a rather different attitude towards it than what I was use to. Re: cost of distilling, the flash type distilling plant uses steam ejectors to lower the pressure in the unit to about ten inches of mercury, at which the boiling point of water is a bit over 120 degrees F. So the heat energy needed was fairly modest when considering the rest of the energy budget of the plant. I use to have to account for 750,000 gallons of No. 2 diesel with a full bag of fuel. Daily consumption was between 35,000 and 50,000 gallons a day with a high of 75,000 a day at full power.

Ed



ff1044@aol.com

The “standard” system, once the technology had coalesced in one direction (say, in the 1860's?) was and is to run with a closed system, i.e., they condense the exhaust steam, filter out any oil and other junk, and pump it back into the boiler. The only water needed was to make up for losses due to leaks, or waste at the safety valve or whistle. This water is carried in tanks built into the hull, and is supplemented by fresh water distilled from sea water by a desalinization plant aboard ship. Adding a pump to the condenser gave the added benefit that the engines could exhaust into a vacuum which gave a substantial increase in power.

Strasburg Rail Road Mechanical Department
kelly@strasburgrailroad.com

Does the Navy use R/O systems now or do they still use the older method of desalination?


captbuck@comcast.net

> Does the Navy use R/O systems now or do they
> still use the older method of desalination?

Are you planning on running a steam locomotive on sea water?



Saturated_steam@yahoo.com

> Does the Navy use R/O systems now or do they
> still use the older method of desalination?

With a lot of waste heat going up the stacks and out the main condensor discharge, the use of R/O hasn't found too many takers in the Navy. Also R/O takes a lot of space as compaired to a distilling plant and space is always at a premium on a ship.

Ed

ff1044@aol.com

> With a lot of waste heat going up the stacks
> and out the main condensor discharge, the
> use of R/O hasn't found too many takers in
> the Navy. Also R/O takes a lot of space as
> compaired to a distilling plant and space is
> always at a premium on a ship.

> Ed

After seeing the new Coast Guard cutter Hollyhock last weekend, I understand that they use the distilling plant method as well. Its a very compact unit, taking up a hold maybe the size of 12 x 12 room near the bow on the Port side. Of course, its a highly computerized unit, and is not really used in the Great Lakes environment, beyond filtering the pollutants out of the "fresh" water when they need it on occassion.

TJG


Port Huron Museum
tjgaffney@phmuseum.org

Two things: Because they are fresh, the GreatLakes and the Inland Rivers got an early jump on ocean ic steam in the 19th century.

Many of the historic steam ships that I know did not use evaporators. They had to carry their own supply of fresh water. The ocean going steam tug Hercules had tanks for fuel oil and water in equal amounts.

To give this a railroad slant,some of the fleets of harbor steam tugs, lighters etc were very much like land steam locos in they used the steam once and exhausted to atmosphere. They were known as "Puffing Billies".

Both labor and coal were cheap, and polution concerns non-existant. The South Street Seaport Museum has such an engine from New York Central 29
in its collection. Unfortunately they could not save the whole lighter, which was the last up and down engine operating in New York harbor.


ted_miles@nps.gov